This is not a hallmark as the spoons are not silver. They may be electroplated or, more likely, a base metal alloy. The manufacturer was J G Graves Ltd of Sheffield. CS probably stands for whatever proprietary name they gave to the metal from which they made the spoons. The company was active between 1900 and 1914 so that fits very neatly with the presentation date of 1911.
Thanks for the information! Greatly appreciated!